1. Field of the Invention
This invention relates to a shock wave treatment apparatus for treating a living body by crushing a gallstone, urinary calculus or the like in the living body with the concentrated energy of shock waves.
2. Description of the Related Art
One type of ultrasonic treatment apparatus is disclosed in Japanese Patent Disclosure (KOKAI) 62-049843. FIG. 1 is a cross section showing an ultrasonic applicator constituting the above ultrasonic treatment apparatus.
As shown in FIG. 1, ultrasonic applicator 1 includes concave transducer 2 having a radius of curvature of 5 cm and having a through hole formed with a predetermined shape in its center, and backing member 3 uniformly formed on the back side of concave transducer 2.
Ultrasonic transducer 4 is a sector probe which is fixed in the through hole and has transducer array 4a of narrow transducer elements arranged in alignment with the concave surface of concave transducer 2.
In FIG. 1, 5 denotes an acoustic coupler constituted by bag 6 which is filled with water and is formed of a thin film having an acoustic impedance substantially equal to that of water.
Further, an ultrasonic treatment apparatus disclosed in article "Die Zertrummerung von Nierensteinen mit einem piezoelektrischen Geratesystem" by M. Ziegler et al, Urologe [A] (1986) 25:193-197 and including ultrasonic applicator 7 shown in FIG. 2 is also used.
Applicator 7 shown in FIG. 2 includes concave transducer 9 which corresponds to concave transducer 2 shown in FIG. 1 and is disposed below bed 8, water tank 10 filled with water and defined by the ultrasonic wave transmission/reception surface of concave transducer 9 and opening 13 formed in bed 8, and ultrasonic applicator 11 disposed inside water tank 10.
In FIG. 2, 12 shows the manner in which the shock wave transmitted from concave transducer 9 is converged.
In general, the above conventional ultrasonic treatment apparatus are understood to have the following defects:
In the ultrasonic treatment apparatus disclosed in Japanese Patent Disclosure (KOKAI) 62-049843, the front end surface of ultrasonic array 4a acting as the ultrasonic wave transmission/reception surface of ultrasonic wave transducer 4 of ultrasonic applicator 1 is arranged in the same curved plane as the ultrasonic wave transmission/reception surface of concave transducer 2 or behind the curved plane.
The quality of the displayed image of a to-be-crushed object is generally dependent on the width of the transmission/reception surface and the distance from the transmission/reception surface to the convergent point. With the above construction, the distance from the transmission/reception surface of ultrasonic wave transducer 4 to the stone is made long because of the presence of water in acoustic coupler 5 and the thin film constituting acoustic coupler 5. Therefore, it is impossible to prevent the ultrasonic wave from being scattered and attenuated, and the displayed image on the display unit will be influenced by noise, making it difficult to correctly recognize the to-be-crushed object.
In contrast, the ultrasonic treatment apparatus disclosed in the article "Urologe [A] (1986) 25:193-197" has the defects caused by use of the mechanical probe. For example, the quality of the displayed image is lowered, the whole size becomes large, it is mechanically weak and easily affected by vibration, and it is difficult to operate the ultrasonic applicator since it is fixedly mounted on the bed.